Numerical modelling of negative corona discharge in SF6at atmospheric pressure

Abstract

This paper presents a numerical simulation of the first negative corona in SF₆ at atmospheric pressure, in a point-to-plane electrode system. A few experiments are first carried out in order to acquire a basic knowledge of the physical processes involved in the first negative corona. Since it does not seem convincing that photoemission would be the predominant secondary process at the cathode surface, field effect emission will be introduced into the numerical modelling of the ignition and development of the first negative corona. The axial and radial development of the discharge is also optically measured. Continuity equations of electron, positive- and negative-ion densities are numerically solved on a non-uniform mesh with a monotonic upwind scheme for conservation law (MUSCL) method. These equations are coupled with Poisson's equation by using the classical method of disks introduced by Davies. The novelty of this model bears upon the choice of the boundary conditions which take field effect emission into account. According to the numerical simulation, this secondary effect could indeed explain the fast rise time of the typical negative corona current pulse, and enables numerical simulation results to be in agreement with the experimental ones.